The loop does not take all values

t=1;
coupj=1;
L  = 4;
d = 3;

N_hole=2:2:-2;
tic
%for nume = 1:length(N_hole)
    Nh = 2;%N_hole(nume)
N_UP=(L-Nh)/2;
N_DN = (L-Nh)/2;


%***************** Basis generation %************************************
%**************** Hamiltonian parameter ********************************
%pbc=1; % pbc=1 ==> PBC, pbc=0 RBC
%sz=0; %Subblock of sz for the computations
Sz0_space=factorial(L)/(factorial(N_UP)*factorial(N_DN)*factorial(Nh))
%***************************************************************************
%Whole basis computation
basis_spin=zeros(d^L,L);
for i1=1:1:L
    ba=0;
    for i2=1:1:d^L
        basis_spin(i2,i1)=ba;
        if mod(i2,d^(L-i1))==0
            ba=mod(ba+1,d);
        end
    end
end

% Chagrge conservation and magnetization conservation
% first we count the number of 1's and 2's in each basis states from
% basis_spin. Then we set condition that if number of 1's = N_UP and number
% of 2's=N_DN then we store those basis from d^L basis states.
szbasis_Ne = zeros(Sz0_space,L);
basis_Ne=zeros(Sz0_space,L);
val=1;
for i2=1:d^L
    Loca1 = basis_spin(i2,:)==1;
    Loca2 = basis_spin(i2,:)==2;
    if (sum(Loca1~=0,2)~=0 && sum(Loca2~=0,2)~=0 && sum(Loca1~=0,2)==N_UP && sum(Loca2~=0,2)==N_DN)
        basis_Ne(val,:)=basis_spin(i2,:);
        order_sz(1,val)=i2-1;
        %order_sz_1(1,val) = bi2de(basis_Ne(val,:), 3,'left-msb');
        val=val+1;
    end
end

dimension = size(basis_Ne);
dimension = dimension(1);




dn_v1 =cell(L,1);

%***********************************************

for i1 = 1:L
    cont1=1;
    if i1==L
     n=1; m=L;
     else
        n=i1; m=i1+1;
    end
    n
    m
   % Loop over the basis elements
    for i2=1:dimension
        if basis_Ne(i2,m)==2 && basis_Ne(i2,n)==0 
           %basis_Ne(i2,:)
           %order_sz(i2)
           basis_Ne(i2,n)=2;
           basis_Ne(i2,m)=0;
           %basis_Ne(i2,:)
           aux_dn = bi2de(basis_Ne(i2,:), 3,'left-msb');
           %aux_dn=order_sz(i2)+(-1)^P*value %Output vector in the whole basis
           out_dn=find(order_sz==aux_dn); %Output vector position in the subblock
            %We construct the matrix and the complex conjugate
           dn_v1{i1}(cont1)=out_dn;
           dn_vc1{i1}(cont1)=i2;
           dn_w1{i1}(cont1)=i2;
           dn_wc1{i1}(cont1)=out_dn;
           cont1=cont1+1;
        end
    end
end

The code does not run for all i2 for i1=L. Could any one help me to figure it out?

[Image Analyst]

You need to learn how to debug. Once you do you will be fully enabled for figuring out these simple things on your own.

Debugging in MATLAB

Just step through and look at what the variable values are and see what lines get executed. Seriously, that's all we would do if we had to do it for you.

[Utkarsh Mishra]

Yes ture. I am trying. But i posted here, in case I am missing very simple things which Ifail to pin point. This last loop should be simple. In fact, if I replace the i1 loop from i1=L:L, surprisingly, it works.

for i1 = 1:L
    cont1=1;
    if i1==L
     n=1; m=L;
     else
        n=i1; m=i1+1;
    end
    n
    m
   % Loop over the basis elements
    for i2=1:dimension
        if basis_Ne(i2,m)==2 && basis_Ne(i2,n)==0 
           %basis_Ne(i2,:)
           %order_sz(i2)
           basis_Ne(i2,n)=2;
           basis_Ne(i2,m)=0;
           %basis_Ne(i2,:)
           aux_dn = bi2de(basis_Ne(i2,:), 3,'left-msb');
           %aux_dn=order_sz(i2)+(-1)^P*value %Output vector in the whole basis
           out_dn=find(order_sz==aux_dn); %Output vector position in the subblock
            %We construct the matrix and the complex conjugate
           dn_v1{i1}(cont1)=out_dn;
           dn_vc1{i1}(cont1)=i2;
           dn_w1{i1}(cont1)=i2;
           dn_wc1{i1}(cont1)=out_dn;
           cont1=cont1+1;
        end
    end
end

Answer 1

[per isakson]

I cannot reproduce the issue that you report. You didn't show us the error message! There is an error message?

First, I tidied your code a bit and added section breaks (%%). Now the code analyzer box is green, , and the section breaks allows me to run the code section by section,

%%
t=1;
coupj=1;
L  = 4;
d = 3;

N_hole=2:2:-2;

Nh = 2; 
N_UP=(L-Nh)/2;
N_DN = (L-Nh)/2;

%% ***************** Basis generation %************************************
%**************** Hamiltonian parameter ********************************
%pbc=1; % pbc=1 ==> PBC, pbc=0 RBC
%sz=0; %Subblock of sz for the computations
Sz0_space=factorial(L)/(factorial(N_UP)*factorial(N_DN)*factorial(Nh));
fprintf( 1, '\nSz0_space = %d\n\n', Sz0_space );
%***************************************************************************
%Whole basis computation
basis_spin=zeros(d^L,L);
for i1=1:1:L
    ba=0;
    for i2=1:1:d^L
        basis_spin(i2,i1)=ba;
        if mod(i2,d^(L-i1))==0
            ba=mod(ba+1,d);
        end
    end
end

%% Chagrge conservation and magnetization conservation
% first we count the number of 1's and 2's in each basis states from
% basis_spin. Then we set condition that if number of 1's = N_UP and number
% of 2's=N_DN then we store those basis from d^L basis states.
szbasis_Ne = zeros(Sz0_space,L);
basis_Ne=zeros(Sz0_space,L);
val=1;
for i2=1:d^L
    Loca1 = basis_spin(i2,:)==1;
    Loca2 = basis_spin(i2,:)==2;
    if  sum(Loca1~=0,2)~=0 && sum(Loca2~=0,2)~=0 ...
    &&  sum(Loca1~=0,2)==N_UP && sum(Loca2~=0,2)==N_DN
        basis_Ne(val,:)=basis_spin(i2,:);
        order_sz(1,val)=i2-1;                                       %#ok<SAGROW>
        %order_sz_1(1,val) = bi2de(basis_Ne(val,:), 3,'left-msb');
        val=val+1;
    end
end

dimension = size(basis_Ne);
dimension = dimension(1);
dn_v1 = cell(L,1);

% %% ***********************************************
% for i1 = 1:L
%     cont1=1;
%     if i1==L
%         n=1; m=L;
%     else
%         n=i1; m=i1+1;
%     end
%     fprintf( 1, '%d, %d\n', n, m );
% 
%     % Loop over the basis elements
%     for i2=1:dimension
%         if basis_Ne(i2,m)==2 && basis_Ne(i2,n)==0
%             %basis_Ne(i2,:)
%             %order_sz(i2)
%             basis_Ne(i2,n)=2;
%             basis_Ne(i2,m)=0;
%             %basis_Ne(i2,:)
%             aux_dn = bi2de(basis_Ne(i2,:), 3,'left-msb');
%             %aux_dn=order_sz(i2)+(-1)^P*value %Output vector in the whole basis
%             out_dn=find(order_sz==aux_dn); %Output vector position in the subblock
%             %We construct the matrix and the complex conjugate
%             dn_v1{i1}(cont1)=out_dn;
%             dn_vc1{i1}(cont1)=i2;
%             dn_w1{i1}(cont1)=i2;
%             dn_wc1{i1}(cont1)=out_dn;
%             cont1=cont1+1;
%         end
%     end
% end
%%  Comment #2
for i1 = 1:L
    cont1=1;
    if i1==L
        n=1; m=L;
    else
        n=i1; m=i1+1;
    end
    fprintf( 1, 'n = %d, m = %d\n', n, m );
    
    % Loop over the basis elements
    fprintf( 1, 'i1, i2,  m,  n, basis_Ne(i2,m), basis_Ne(i2,n), aux_dn\n' );
    for i2=1:dimension
        if basis_Ne(i2,m)==2 && basis_Ne(i2,n)==0
            %basis_Ne(i2,:)
            %order_sz(i2)
            basis_Ne(i2,n)=2;
            basis_Ne(i2,m)=0;
            %basis_Ne(i2,:)
            aux_dn = bi2de(basis_Ne(i2,:), 3,'left-msb');
            fprintf( '%2d,%3d,%3d,%3d,%15d,%15d, %f\n'              ...
                    ,i1,i2,m,n,basis_Ne(i2,m),basis_Ne(i2,n),aux_dn' );

            %aux_dn=order_sz(i2)+(-1)^P*value %Output vector in the whole basis
            out_dn=find(order_sz==aux_dn); %Output vector position in the subblock
            %We construct the matrix and the complex conjugate
            dn_v1{i1}(cont1)=out_dn;
            dn_vc1{i1}(cont1)=i2;       %#ok<SAGROW>
            dn_w1{i1}(cont1)=i2;        %#ok<SAGROW>
            dn_wc1{i1}(cont1)=out_dn;   %#ok<SAGROW>
            cont1=cont1+1;
        else
            fprintf( '%2d,%3d,%3d,%3d,%15d,%15d\n'          ...
                    ,i1,i2,m,n,basis_Ne(i2,m),basis_Ne(i2,n)' );
        end
    end
    fprintf('\n');
end

This script outputs

Sz0_space = 12

n = 1, m = 2
i1, i2,  m,  n, basis_Ne(i2,m), basis_Ne(i2,n), aux_dn
 1,  1,  2,  1,              0,              0
 1,  2,  2,  1,              0,              0
 1,  3,  2,  1,              1,              0
 1,  4,  2,  1,              1,              0
 1,  5,  2,  1,              0,              2, 55
 1,  6,  2,  1,              0,              2, 57
 1,  7,  2,  1,              0,              1
 1,  8,  2,  1,              0,              1
 1,  9,  2,  1,              2,              1
 1, 10,  2,  1,              0,              2
 1, 11,  2,  1,              0,              2
 1, 12,  2,  1,              1,              2

n = 2, m = 3
i1, i2,  m,  n, basis_Ne(i2,m), basis_Ne(i2,n), aux_dn
 2,  1,  3,  2,              1,              0
 2,  2,  3,  2,              0,              2, 19
 2,  3,  3,  2,              0,              1
 2,  4,  3,  2,              2,              1
 2,  5,  3,  2,              0,              0
 2,  6,  3,  2,              1,              0
 2,  7,  3,  2,              0,              0
 2,  8,  3,  2,              0,              2, 45
 2,  9,  3,  2,              0,              2
 2, 10,  3,  2,              0,              0
 2, 11,  3,  2,              1,              0
 2, 12,  3,  2,              0,              1

n = 3, m = 4
i1, i2,  m,  n, basis_Ne(i2,m), basis_Ne(i2,n), aux_dn
 3,  1,  4,  3,              2,              1
 3,  2,  4,  3,              1,              0
 3,  3,  4,  3,              0,              2, 15
 3,  4,  4,  3,              0,              2
 3,  5,  4,  3,              1,              0
 3,  6,  4,  3,              0,              1
 3,  7,  4,  3,              0,              2, 33
 3,  8,  4,  3,              0,              0
 3,  9,  4,  3,              0,              0
 3, 10,  4,  3,              1,              0
 3, 11,  4,  3,              0,              1
 3, 12,  4,  3,              0,              0

n = 1, m = 4
i1, i2,  m,  n, basis_Ne(i2,m), basis_Ne(i2,n), aux_dn
 4,  1,  4,  1,              0,              2, 57
 4,  2,  4,  1,              1,              0
 4,  3,  4,  1,              0,              0
 4,  4,  4,  1,              0,              0
 4,  5,  4,  1,              1,              2
 4,  6,  4,  1,              0,              2
 4,  7,  4,  1,              0,              1
 4,  8,  4,  1,              0,              1
 4,  9,  4,  1,              0,              1
 4, 10,  4,  1,              1,              2
 4, 11,  4,  1,              0,              2
 4, 12,  4,  1,              0,              2

[Utkarsh Mishra]

There is no error message. I am interested in output of this part.

aux_dn = bi2de(basis_Ne(i2,:), 3,'left-msb');

Whenever, i1=1:3, the above output runs correct as i checked, the below condition is satisfied

 if basis_Ne(i2,m)==2 && basis_Ne(i2,n)==0

For i1=L, the above ondition is satisfied by two values of i2, so I should get two values from the belwo output

aux_dn = bi2de(basis_Ne(i2,:), 3,'left-msb');

But, the i1=L loop just give me one value.

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

Output for i1=L:L

Sz0_space =

12

i2 =

1

aux_dn =

57

i2 =

3

aux_dn =

63

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

But for i1=1:L, and when i1=L, the loop over i2 gives only one value. (When i1=1:L-1, n=i1, m=1i1+1, but when i1=L, n=1, m=L)

i2 =

1

aux_dn =

57

So, I don't understand why the loop over i2 does not takes all possible values for the cindition

 if basis_Ne(i2,m)==2 && basis_Ne(i2,n)==0

when i1=1:L.

[per isakson]

It's often easier to understand with a better debug print output.

I've modified the output of the script in my answer.

[Utkarsh Mishra]

Thanks. But for i=L:L, the output is different from i=1:L. This is the one I coult not figure out.

Sz0_space =

    12

n = 1, m = 4
i1, i2,  m,  n, basis_Ne(i2,m), basis_Ne(i2,n), aux_dn
 4,  1,  4,  1,              0,              2, 57
 4,  2,  4,  1,              1,              0
 4,  3,  4,  1,              0,              2, 63
 4,  4,  4,  1,              0,              0
 4,  5,  4,  1,              1,              0
 4,  6,  4,  1,              0,              0
 4,  7,  4,  1,              2,              1
 4,  8,  4,  1,              0,              1
 4,  9,  4,  1,              0,              1
 4, 10,  4,  1,              1,              2
 4, 11,  4,  1,              0,              2
 4, 12,  4,  1,              0,              2

[per isakson]

I've modified the print-statements so that the first part is printed directly before the if-statement.

    % Loop over the basis elements
    fprintf( 1, 'i1, i2,  m,  n, basis_Ne(i2,m), basis_Ne(i2,n), aux_dn\n' );
    for i2=1:dimension
        fprintf( '%2d,%3d,%3d,%3d,%15d,%15d,'           ...           
                ,i1,i2,m,n,basis_Ne(i2,m),basis_Ne(i2,n) );
        if basis_Ne(i2,m)==2 && basis_Ne(i2,n)==0
            %basis_Ne(i2,:)
            %order_sz(i2)
            basis_Ne(i2,n)=2;
            basis_Ne(i2,m)=0;
            %basis_Ne(i2,:)
            aux_dn = bi2de(basis_Ne(i2,:), 3,'left-msb');
            fprintf( '%7d\n', aux_dn );

            %aux_dn=order_sz(i2)+(-1)^P*value %Output vector in the whole basis
            out_dn=find(order_sz==aux_dn); %Output vector position in the subblock
            %We construct the matrix and the complex conjugate
            dn_v1{i1}(cont1)=out_dn;
            dn_vc1{i1}(cont1)=i2;       %#ok<SAGROW>
            dn_w1{i1}(cont1)=i2;        %#ok<SAGROW>
            dn_wc1{i1}(cont1)=out_dn;   %#ok<SAGROW>
            cont1=cont1+1;
        else
            fprintf('\n');
        end
    end

Now I get the following to outputs for i1==4 .

>> n = 1, m = 4
i1, i2,  m,  n, basis_Ne(i2,m), basis_Ne(i2,n), aux_dn
 4,  1,  4,  1,              2,              0,     57
 4,  2,  4,  1,              1,              0,
 4,  3,  4,  1,              0,              0,
 4,  4,  4,  1,              0,              0,
 4,  5,  4,  1,              1,              2,
 4,  6,  4,  1,              0,              2,
 4,  7,  4,  1,              0,              1,
 4,  8,  4,  1,              0,              1,
 4,  9,  4,  1,              0,              1,
 4, 10,  4,  1,              1,              2,
 4, 11,  4,  1,              0,              2,
 4, 12,  4,  1,              0,              2,

n = 1, m = 4
i1, i2,  m,  n, basis_Ne(i2,m), basis_Ne(i2,n), aux_dn
 4,  1,  4,  1,              2,              0,     57
 4,  2,  4,  1,              1,              0,
 4,  3,  4,  1,              2,              0,     63
 4,  4,  4,  1,              0,              0,
 4,  5,  4,  1,              1,              0,
 4,  6,  4,  1,              0,              0,
 4,  7,  4,  1,              2,              1,
 4,  8,  4,  1,              0,              1,
 4,  9,  4,  1,              0,              1,
 4, 10,  4,  1,              1,              2,
 4, 11,  4,  1,              0,              2,
 4, 12,  4,  1,              0,              2,

Yes, the two differs on the third line. And that's because the condition of the if-statement returns false in the first case and true in the second. And most likely that is because in the first iteration of the for-loop basis_Ne is modified inside the if-clause by the two statements

basis_Ne(i2,n)=2;
basis_Ne(i2,m)=0;

(you might need to read this twice).

[Utkarsh Mishra]

Yes, now I got it.